major refactor to absorb defunct libcollections collections

* Updates `traverse` because of latest nightly
* Renames and shuffles modules to match conventions
* Re-exports collections at the top level
* Steals Tree\*, Trie\*, LruCache, and EnumSet from libcollections

CC @aturon
probably bes to rely on `^0.0.0` or `*` at this point.